Here, we report on two patients with hemorrhagic shock due to hematemesis from a gastrointestinal stromal tumor (GIST) of the stomach. Patient 1 was a 64-year-old woman who was admitted to our hospital because of syncope due to hemorrhagic shock resulting from massive hematemesis. Emergent upper gastrointestinal (GI) endoscopy revealed a 5-cm-diameter submucosal tumor on the lesser curvature of the lower gastric body. In addition to the central ulceration of the tumor, a Dieulafoy-like lesion was present. Neither lesions showed active bleeding at the time of observation. Because the patient collapsed twice with fluminant hematemesis after admission, she underwent distal gastrectomy with Billroth-I reconstruction. Histological examination revealed a gastric GIST with no nodal metastasis and the mitotic count was less than 5 per 50 HPFs. Dilated vessels were prominent in the peritumoral submucosa, and a thrombus was seen in these vessels, which seemed to be a bleeding point. The patient had an uneventful postoperative course and has been alive without recurrence for 5 and a half years. Patient 2 was a 60-year-old man who presented with syncope due to hemorrhagic shock resulting from massive hematemesis. Because the source of the bleeding was not elucidated with an initial upper GI endoscopy, he was treated for a gastric ulcer. One week after admission, he suffered from hemorrhagic shock again, and a submucosal tumor 6 cm in size was revealed on the greater curvature of the upper stomach with upper GI endoscopy. The patient subsequently underwent wedge resection of the tumor. Histopathological findings were consistent with a GIST and the mitotic count was less than 5 per 50 high-power fields. The tumor showed no necrosis or intratumoral hemorrhage. A peritumoral submucosal artery, which was responsible for the massive hematemesis, was located at some distance away from the central ulceration. Postoperative recovery was without complications. After 4 years, the patient remains healthy and disease-free. Although hematemesis associated with gastric GIST has been said to originated from the central ulceration of the GIST, life-threatening, massive hematemesis is rare. The exact bleeding points of the gastric GISTs in these cases were submucosal vessels adjacent to the GIST, not the central ulceration. There have been no reports of peritumoral, submucosal vessels causing massive hematemesis from gastric GISTs. Because the origins and manner of bleeding varies in gastric GISTs, we must decide the methods of hemostasis immediately including the tumor excision.